The present invention relates to an ion source, a mass spectrometer, a method of ionising ions and a method of mass spectrometry.
Impactor spray atmospheric pressure ionisation (“API”) ion sources are known and comprise an arrangement wherein a heated, high velocity liquid spray is emitted from a nebuliser and is directed so as to impact upon a small cylindrical rod target that is held at a relatively high potential with respect to the nebuliser. The resulting plume from the target is then sampled into the first vacuum stage of a mass spectrometer for subsequent mass analysis.
Conventional atmospheric pressure ionisation ion sources typically use a curtain or cone gas that creates a gas flow between the ion inlet and the ionisation probe that is countercurrent to the direction of the ions and charged particles emanating from the probe.
The curtain or cone gas reduces the effects of ion inlet contamination and this is particularly useful for low cost instruments that utilise relatively small inlet orifices (≤0.2 mm). Additionally, the curtain or cone gas can reduce the level of background chemical noise by preventing neutral contaminants (reactants or adducting agents) from entering the mass spectrometer.
A problem with the known arrangement is that if the cone gas flow is maintained at a flow rate which exceeds the flow of gas being drawn through the inlet into the first vacuum stage of the mass spectrometer then ion signal losses can become significant.
Accordingly, known impactor spray ion sources suffer from a loss of ion signal at high cone gas flow rates which is particularly problematic.
WO2012/143737 (Micromass) discloses an impactor spray atmospheric pressure ionisation (“API”) ion source.
WO2013/098642 (Szalay) discloses a collision ion generator and separator.
WO2010/045049 (Ouyang) discloses systems and methods for transfer of ions for analysis.
WO2007/138371 (Takats) discloses an arrangement for desorption ionisation by liquid jet.
EP1855306 (Cristone) discloses an ionisation source and method for mass spectrometry.
U.S. Pat. No. 5,986,259 (Hirabayashi) discloses a mass spectrometer.
US2006/0108539 (Franzen) discloses an arrangement of ionisation by droplet impact.
US2009/0278036 (Wollnik) discloses a droplet pickup ion source coupled to mobility analyser apparatus and method.
JP2002/190272 (Susumu) discloses an electron-spray ion source.
US2003/0119193 (Hess) discloses a system and method for high throughput screening of droplets.
It is desired to provide an improved ion source and an improved method of ionising ions.